Do top universities allow just 3 A levels including Further Maths?

I'm currently in Y12 studying Maths, Further Maths and Computer Science. I want to apply to top unis for Computer Science like Cambridge, Imperial & UCL, but I'm anxious that having Further Maths as my third subject is going to reduce my chances of getting an offer from these universities.

Just taking Imperial as an example, (and they don't have a pure COMPSCI programme, it's Computing or Maths with COMPSCI). For BEng Computing the answer is that FM is accepted just fine as a third subject.
https://www.imperial.ac.uk/study/courses/undergraduate/computing-beng/
"A*A*A – A*AAA
To include:
A* in Mathematics
A*, A in two further subjects or AAA in three further subjects, with Further Mathematics preferred."
Most uni websites should make it clear where they stand on FM as a third/fourth subject as it is a common question. But it will be a bit of legwork to review their websites.

It takes minutes to review entry requirements on each website. You open up each uni website to the entry requirements page, which is a few clicks and compare. Done in less than 10 minutes and you know you're getting accurate information.